diff --git a/src/common/os.cpp b/src/common/os.cpp
index 3822ad240..692ebbd0d 100644
--- a/src/common/os.cpp
+++ b/src/common/os.cpp
@@ -21,42 +21,41 @@
 #include <malloc.h>
 #include <string.h>
 
-int
-vsscanf(const char *buffer,
-        const char *format,
-        va_list argPtr) {
-  // Get an upper bound for the # of args
-  size_t count = 0;
-  const char *p = format;
-  while (1) {
-    char c = *(p++);
-    if (c == 0)
-      break;
-    if ((c == '%') && ((p[0] != '*') && (p[0] != '%')))
-      ++count;
-  }
+int __declspec(naked) vsscanf_impl(const char *,const char *,va_list,int,void *) {
+  __asm {
+    push    ebx
+    mov	    ebx,esp
+    mov	    ecx,[ebx+16]
+    mov	    edx,[ebx+20]
+    lea	    edx,[ecx+edx*4-4]
+    jmp	    l3
+l2:
+    push    dword ptr [edx]
+    sub	    edx,4
+l3:
+    cmp	    edx,ecx
+    jae	    l2
+    push    dword ptr [ebx+12]
+    push    dword ptr [ebx+8]
+    call    dword ptr [ebx+24]
+    mov	    esp,ebx
+    pop	    ebx
+    ret
+  };
+}
 
-  // Make a local stack
-  size_t stackSize = (2 + count) * sizeof(void *);
-  void **newStack = (void **)alloca(stackSize);
+int vsscanf(const char *str, const char *format, va_list ap) {
+  const char  *p = format;
+  int	      narg = 0;
 
-  // Fill local stack the way sscanf likes it
-  newStack[0] = (void*)buffer;
-  newStack[1] = (void*)format;
-  memcpy(newStack + 2, argPtr, count * sizeof(void *));
+  while (*p)
+    if (*p++ == '%') {
+      if (*p != '*' && *p != '%')
+	++narg;
+      ++p;
+    }
 
-  // Warp into system sscanf with new stack
-  int result;
-  void *savedESP;
-  _asm {
-    mov     savedESP, esp;
-    mov     esp, newStack;
-    call    sscanf;
-    mov     esp, savedESP;
-    mov     result, eax;
-  }
-
-  return result;
+  return vsscanf_impl(str,format,ap,narg,sscanf);
 }
 
 #endif
diff --git a/src/merge/mkvmerge.h b/src/merge/mkvmerge.h
index 6e560fbbb..6978fd13f 100644
--- a/src/merge/mkvmerge.h
+++ b/src/merge/mkvmerge.h
@@ -26,7 +26,7 @@ enum display_priority_e {
 
 /* file types */
 enum file_type_e {
-  FILE_TYPE_UNKNOWN = 0,
+  FILE_TYPE_IS_UNKNOWN = 0,
   FILE_TYPE_OGM,
   FILE_TYPE_AVI,
   FILE_TYPE_WAV,
diff --git a/src/merge/output_control.cpp b/src/merge/output_control.cpp
index 636b3c791..de98a9e3d 100644
--- a/src/merge/output_control.cpp
+++ b/src/merge/output_control.cpp
@@ -269,7 +269,7 @@ get_file_type(const string &filename) {
             filename.c_str());
   }
 
-  type = FILE_TYPE_UNKNOWN;
+  type = FILE_TYPE_IS_UNKNOWN;
   if (avi_reader_c::probe_file(mm_io, size))
     type = FILE_TYPE_AVI;
   else if (kax_reader_c::probe_file(mm_io, size))
@@ -324,7 +324,7 @@ get_file_type(const string &filename) {
     else if (vobsub_reader_c::probe_file(mm_text_io, size))
       type = FILE_TYPE_VOBSUB;
     else
-      type = FILE_TYPE_UNKNOWN;
+      type = FILE_TYPE_IS_UNKNOWN;
 
     mm_io = mm_text_io;
   }